Electric contacts that mechanically switch electric circuits have been used as components of various switches or relays of electric equipment in a wide range of fields from home appliances, OA equipment, electric parts for automobiles, and the like to heavy electric machinery. As the switching-type electric contacts, there is a tip-shaped contact that is directly joined to a support member such as a spring member, but a rivet contact is generally used in many cases. The rivet contact includes a head portion acting as an electric contact and a foot portion having a smaller width than the head portion. The foot portion is deformed by a caulking when the rivet contact is fixed to the support member.
Then, the electric contact is required to be capable of maintaining reliable mechanical switching, that is, capable of transmitting current and signal flowing to the contact without hindrance at the time of contacting and be separated without hindrance at the time of disconnection. Further, the electric contact is also required to have a stable contact resistance. On the other hand, melting, evaporation, consumption, and the like of the material due to discharge occur on a surface of the switching contact. These phenomena inhibit a contacting function of the electric contact and sometimes fuse the contacts together. These become factors of causing performance deterioration or a breakdown of an electric product or the like. For this reason, many studies also have been made on constituent materials in order that the electric contact becomes capable of performing the basic functions described above even under such severe loads. Among them, a suitable contact material is currently considered an Ag-based contact material, and in particular, an oxide-dispersed Ag alloy (Ag—SnO2 alloy, Ag—SnO2—In2O3 alloy, Ag—ZnO alloy, or the like) having various metal oxides such as SnO2, In2O3, and CuO dispersed in an Ag matrix is often applied.
The entire structure of the conventional rivet contact is often formed of a contact material. However, recently, in consideration of the expensive contact material such as the Ag alloy, it has been general to use a double-layered rivet contact in which the contact material is applied to a portion of the contact in order to reduce a cost of a member and a relatively low-cost material (base material) such as Cu and a Cu alloy constitutes other portions of the contact.
As such a double-layered rivet contact having a combination of the Ag alloy and the Cu-based material, there are known, for example, a rivet contact in which a contact material constitutes a top portion of a head portion and a base material such as Cu constitutes a bottom of the head portion and a foot portion (FIG. 7(a), see Patent Document 1), and a rivet contact in which a contact material constitutes the entire head portion and a base material constitutes a foot portion (FIG. 7(b), see Patent Document 2).